Temperature sensitive, conditional lethal mutants of a variant of Pichinde virus, Pichinde Munchique, which has two genome segments (L and S), and three major virion polypeptide (N, G1 and G2) easily distinguished from their counterparts of the prototype Pichinde virus, will be used in dual mutant virus infections with mutants of the prototype virus to derive wild-type recombinant viruses. The recombinants produced will be analysed at the genome and polypeptide level to determine if they are reassortant, revertant or intramolecular recombinant genotypes and their virion polypeptides analysed to determine the viral RNA gene product coding assignments.